If this is false, can he sue?
Anyone can sue...would he be successful? It depends...he is a public figure so his standard of proof for defamation or libel is different than you or I. Part of the issue is that nothing is really being said other than there is something out there that is bad. Depending on the jurisdiction the elements for defamation are a statement of fact, that is false, unprivileged, having the natural tendency to cause injury and the person who published it was at least negligent in doing so.
At this point there is no real statement of fact, false or otherwise. It may be argued that equating it to Ray Rice is an issue, but it's hard to say. What exactly is 5x times worse than Ray Rice??? In addition, the last element is hard to prove as well. Negligence has its own set of elements that need to be shown, specifically, duty, breach, causation and damages. If this guys source is credible then is it unreasonable that he would post it? Breaching a duty of general care is a question left for the finders of fact.
He may also potentially have a case for interference with business relationships depending on the circumstances and the nature of how this is all going down.
At the end of the day this is a crappy situation for Dez and I would imagine if it blows over he would just let it go.